Electrical motors are often produced having a cylindrical frame and a series of field assemblies rigidly affixed to an inside wall of the motor frame. A rotor is centrally disposed within the frame and rotates about an axis of the motor. Each field assembly includes a winding and a pole member. The winding has a central aperture that receives a portion of the pole member. The pole member is composed of many layers of metal plates (e.g., laminations) that are fastened together by rivets or bolts. The pole member typically presents sharp comers, metal burrs, or rivet or bolt heads that may protrude from the surface of the pole member. These corners, burrs, and fastener heads, in conjunction with vibration produced during operation of the motor, tend to abrade the insulation of the winding. This leads to grounding or shorting of the winding.
To prevent grounding of the winding, field assemblies have been produced using costly and labor-intensive methods to insulate the winding. The winding is typically formed of copper wire that is machine wound with glass tape or other material to insulate the winding from the pole member. The taped winding is fitted on the pole member and the assembly is then dipped in a varnish bath. However, the process of applying the glass tape is expensive, and care must be taken to insure that the glass tape is not ripped by any sharp edges. Additionally, constant vibration of the motor may eventually cause grounding of the winding if the glass tape becomes sufficiently abraded.
In other cases, sheets of insulating material, such as NOMEX or MYLAR, are inserted between the winding and the pole member to insulate the winding from the pole member. Again, such processes are labor-intensive as the sheets must be placed in the proper location and held in place until fully secured. Additionally, insulating sheets do not always fully insulate the winding from the pole member after prolonged use of the motor, resulting in a grounded winding.